Amazon: 5v power supply circuit Amazon: 5v power supply circuit. Skip to main content. Foval Power Step Down 220V to 110V Voltage Converter with 4-Port USB International Power Travel Adapter in UK European Italy Asia etc, More Than 150 Countries Over The World. 4.3 out of 5 stars 787. $37 $ 37. 60 $39 $ 39. 99. How to Use 5V DC Power Supply from Computer USB Aug 30, 2015Computer’s USB is a good power source for 5v DC regulated supply. Also when there is a circuit which consist motor like DC motor , Servo etc., it’s difficult to run them with a normal 9v battery, especially when battery have gotten weak.